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Abstract

GeO2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO2 laser. The effects of CO2 laser processing on the optical and structural properties of the waveguides were evaluated by different techniques including m-line, micro-Raman spectroscopy, atomic force microscopy, and positron annihilation spectroscopy. After laser annealing, an increase of the refractive index of approximately 0.04 at 1.5 µm and a decrease of the attenuation coefficient from 0.9 to 0.5 db/cm at 1.5 µm was observed. Raman spectroscopy and microscopy results put in evidence that the system embeds GeO2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 µm thickness. In addition, a density value of the amorphous GeO2 samples was evaluated.

Figures (4)

AFM images of representative 1.8 x 1.8 µm2 areas of the samples in the conditions: (a) as prepared and (b) after 2h of CO2 laser irradiation. Z scale 10 nm. In (c) a comparison of typical height profiles in these two conditions, corresponding to sections 1 in panels (a) and (b), showing a decrease in roughness after irradiation is presented. (d) profiles of the nanometric structures found after irradiation - sections 2 and 3 in panel (b).

Normalized shape parameter Sn as a function of the positron implantation energy for the as prepared and after 2h CO2 laser irradiated GeO2 samples. In the upper scale the mean positron implantation depth is reported. Solid lines represent the best fit obtained using the VEPFIT program (see text). The vertical dash-dotted line points out the interface limit between the film and the silica substrate.

Scheme of the nanostructural transformation of the GeO2 films as a function of the depth measured from the surface of the sample and the irradiation time. As shown in this scheme, besides the silica substrate (ρ = 2.1 g/cm3) different layers in the GeO2 films are detected by positron spectroscopy. From the fitting of the positron data reported in Fig. 3, a density value of ρ = 3.15 g/cm3 for the GeO2 was obtained (see text).

Tables (2)

Table 2 Sn values characterizing each layer in the as prepared and the two irradiated samples, as obtained by fitting the positron depth profiles. The density value of the GeO2 film was used as a guess parameter into the frame of the fitting procedure. The boundary depths are measured from the surface of the sample.

Metrics

Table 1

Optical parameters for the samples as prepared and after CO2 laser irradiation for 2h.

Laser wavelength(nm)

Refractive Index

thickness(µm)

Attenuation coefficient(dB/cm)

TE

TM

632

beforeirradiation

1.614 ± 0.001

1.616 ± 0.001

1.1 ± 0.1

1.9 ± 0.2

afterirradiation

1.652 ± 0.001

1.653 ± 0.001

1.1 ± 0.1

1.1 ± 0.2

1319

beforeirradiation

1.590 ± 0.01

1.590 ± 0.01

1.0 ± 0.1

1.4 ± 0.2

afterirradiation

1.631 ± 0.01

1.634 ± 0.01

1.0 ± 0.1

0.7 ± 0.2

1542

beforeirradiation

1.585 ± 0.01

1.585 ± 0.01

1.0 ± 0.1

0.9 ± 0.2

afterirradiation

1.623 ± 0.01

1.624 ± 0.01

1.0 ± 0.1

0.5 ± 0.2

Table 2

Sn values characterizing each layer in the as prepared and the two irradiated samples, as obtained by fitting the positron depth profiles. The density value of the GeO2 film was used as a guess parameter into the frame of the fitting procedure. The boundary depths are measured from the surface of the sample.

Sample

layer Iρ = 3.15 g/cm3

layer IIρ = 3.15 g/cm3

layer IIIρ = 3.15 g/cm3

bulkρ = 2.1 g/cm3

Sn

depth (nm)

Sn

depth (nm)

Sn

depth (nm)

Sn

before irradiation

1.006

11 ± 2

0.952

983 ± 20

–

–

1.000

after 1h irradiation

1.003

2 ± 0.2

0.946

320 ± 25

0.966

983

1.000

after 2h irradiation

0.980

5 ± 0.1

0.950

175 ± 32

0.960

983

1.000

Tables (2)

Table 1

Optical parameters for the samples as prepared and after CO2 laser irradiation for 2h.

Laser wavelength(nm)

Refractive Index

thickness(µm)

Attenuation coefficient(dB/cm)

TE

TM

632

beforeirradiation

1.614 ± 0.001

1.616 ± 0.001

1.1 ± 0.1

1.9 ± 0.2

afterirradiation

1.652 ± 0.001

1.653 ± 0.001

1.1 ± 0.1

1.1 ± 0.2

1319

beforeirradiation

1.590 ± 0.01

1.590 ± 0.01

1.0 ± 0.1

1.4 ± 0.2

afterirradiation

1.631 ± 0.01

1.634 ± 0.01

1.0 ± 0.1

0.7 ± 0.2

1542

beforeirradiation

1.585 ± 0.01

1.585 ± 0.01

1.0 ± 0.1

0.9 ± 0.2

afterirradiation

1.623 ± 0.01

1.624 ± 0.01

1.0 ± 0.1

0.5 ± 0.2

Table 2

Sn values characterizing each layer in the as prepared and the two irradiated samples, as obtained by fitting the positron depth profiles. The density value of the GeO2 film was used as a guess parameter into the frame of the fitting procedure. The boundary depths are measured from the surface of the sample.